1. Field of the Invention
The invention relates to a device for operation of a discharge lamp of the short arc type. The invention relates especially to a device for operation of a discharge lamp of the short arc type which is used for a rear projector device using an LCD device or a DLP (digital light processor) using a DMD (digital mirror device).
2. Description of the Prior Art
In a projection type projector device, there is a demand for illumination of images onto a rectangular screen in a uniform manner and with sufficient color rendering. Therefore, a discharge lamp with a high mercury vapor pressure, for example, with 150 atm, is used as the light source. Here, by increasing the mercury vapor pressure, broadening of the arc is suppressed (the arc is contracted) and an increase of the light intensity as strong as possible is attempted. This type of discharge lamp is disclosed, for example, in Japanese patent disclosure document JP-A-2-148561 and corresponding U.S. Pat. No. 5,109,181, Japanese patent disclosure document JP-A-6-52830 and corresponding U.S. Pat. No. 5,497,049 and Japanese patent JP-B-2980882 and corresponding U.S. Pat. No. 6,271,628 B1.
In the above described discharge lamp, for example, in a silica glass arc tube containing at least 0.15 mg/mm3 of mercury, a rare gas and from 1×10−6 μmole/mm3 to 1×10−2 mole/mm3 of a halogen, there is a pair of opposed electrodes at a distance from one another of at most 2 mm. The main purpose of adding the halogen is to prevent devitrification of the arc tube. However, this also yields occurrence of the so-called halogen cycle.
In a discharge lamp of the short arc type (hereinafter also called only a “discharge lamp”), over the course of operation, the tungsten of which the electrodes are made is transported to the inner side of the discharge vessel and is deposited on it (so-called blackening of the tube wall). This blackening of the tube wall causes a reduction of light intensity, and in a drastic case, can adversely affect the service life of the lamp, such as by damaging the discharge vessel.
On the other hand, a projection type projector device, to date, has been used mainly commercially or for similar purposes as a data projector. The time interval from the end of use of the projector device to the next start of use was at least one minute. This means that there was also at least 1 minute after turning off the discharge lamp until the next operation. With this time interval, the electrode temperature of the discharge lamp can be adequately reduced, by which damage to the electrodes upon restart (at the next operation) is also kept low.
In the course of improving projector technology, however, recently, instead of data projectors, so-called rear projection televisions have appeared which are used like televisions. Their use together with plasma screen televisions and large liquid crystal display televisions is generally expected to be common for home use. In these rear projection televisions, the time interval from the end of the use of the projector device to the next use is shorter than in a data projector. Specifically, there is a demand for an extremely short time within 30 seconds.